原式=[(x+2)(x+12)][(x+3)(x+8)]-4x²
=[(x²+24)+14x][(x²+24)+11x]-4x²
=(x²+24)²+25x(x²+24)+154x²-4x²
=(x²+24)²+25x(x²+24)+150x²
=(x²+24+10x)(x²+24+15x)
=(x+4)(x+6)(x²+15x+24)